Computers can be connected via Amateur Radio, using any computer
code. Simple plain text messages can be sent, or graphics files or
programs. The faster the data transfer rate required, the larger the
channel bandwidth required.

Packet Data using the AX.25 data protocol was invented in 1984 and was very popular in the
1990s. It was a pre-runner of the internet and e-mail.
Messages (or files) could be exchanged on a one to one basis, or on an
international network. The advantage (like e-mail, but unlike instant
messaging systems) was that you didn't need to be present to receive a message.

X.25 is an international packet data switching protocol which is/was used on
wired computer networks and later formed the basis of the internet. AX.25
is a variation of X.25, adapted for Amateur Radio usage. Each packet
(piece) of data contains the address (callsign) of the destination station and
the originating station, as well as the actual message or part of message.
Computer hardware and software can switch the data packets this way or that, to
get them to their destination. If a wired link or a radio link fails, the
data packets are instantly and automatically re-routed, as long as alternative
routes exist.

At the originating end, a long message (e.g. text or picture) is sent as a
stream of individual data packets. Each packet may use a different route
to get to its destination. When all the packets arrive at their
destination, they are joined together to reproduce the original message.

The national network consists of VHF and UHF packet switching nodes, situated
in good locations, with good radio paths to one or more other nodes. The
packet switching nodes link to either each other, or to mailboxes. A
mailbox is a computerised Amateur Radio station which stores messages for
others. When they have time, Radio Amateurs connect to their local mailbox
via radio and check if there are any messages waiting for them. In
addition to personal messages sent to a particular callsign, which could be
downloaded only by the correct callsign, public bulletin messages can be sent
which can be read by anybody.

The packet data network still exists, but interest has severely waned due to
the common, cheap and easy availability of e-mail internet messages. The
packet data network is world wide and every mailbox and node was established and
maintained by volunteers expending vast amounts of their time and money to help
the system work as a whole. The data transfer speeds have to be standard
so that the different equipment will work together. Upgrading a local,
national and international network to compete with broadband internet speeds of
2 Mbps or 8 Mbps is unrealistic, although on a limited or local basis, it is
possible.